DESCRIPTION (Investigator's abstract): The long-term objective of these studies are to better understand the neural control of the pupil. When light is shone in one eye, pupilloconstriction occurs in both eyes and is termed the pupillary light reflex (PLR). With near viewing, convergence and accommodation are accompanied by a pupilloconstriction that is termed the pupillary near response. These pupillary responses are extremely useful to clinicians diagnosing the nature, severity, and extent of brain damage. Furthermore, detailed knowledge of the anatomy and physiology of the subcortical and cortical pathways involved in these pupillary responses is essential if the fledgling field of objective visual field testing using pupillometry (pupil perimetry) is to advance significantly. Unfortunately, there have been few recent studies of the neural control of these pupillary responses. Indeed, to my knowledge, our laboratory is currently only one of two in the world carrying out such up-to-date studies in alert, behaving primates. Therefore, despite the clinical importance of these pupillary responses, the literature is forced to rely on the results of experimental work that was mostly carried out before the advent of modern techniques. Hence, despite our recent extensive studies of the subcortical pupillary pathway in primates, there is still little or no data on the characteristics of the retinal ganglion cells that mediate the PLR, on the influences of the brainstem on the PLR, or on the role of the cerebral cortex in the PLR. To address these issues, we will use electrophysiological, anatomical, and pharmacological techniques in alert, behaving rhesus monkeys. We propose to determine the physiology, morphology, and immunohistochemical characteristics of the retinal ganglion cells that project to the pretectal olivary nucleus, the pretectal nucleus that mediates the PLR. We will characterize the brainstem afferents to this nucleus and the neurotransmitters within it. We will investigate the role of the cerebral cortex in influencing the PLR, we will study the effects of reversible and permanent lesions of striate cortex. In addition, permanent lesions of the dorsal prelunate gyrus will be used to study its involvement in the PLR. We will also use anatomical and electrophysiological techniques to investigate projections from the prelunate gyrus and other extrastriate visual areas to the pretectal olivary nucleus.